(1) Field of the Invention
This invention relates to a communication system and, more particularly, to a communication system for audio communication over a network.
(2) Description of the Related Art
Recently, as more access circuits including xDSLs, cable internets, optical fibers, and wireless circuits are used in a broadband and network-related devices become increasingly sophisticated, the broadband spreads rapidly. This results in offering various applications and services on an Internet Protocol (IP) network.
Specifically, IP phone (Internet phone) services come into practical use, which realize audio communication over IP networks with a Voice over IP (VoIP) technology. Instead of the existing telephones, IP phones are considered as the feature for cheap communication. Therefore, as a network technology advances, IP phones will increasingly spread.
As the IP phone services spread, more users use both the IP phone services and the mobile phone services. For example, while an IP phone system is set up so as to cover all branches of a company, workers move around with their mobile phones.
There is a conventional technique for Internet phones in which a called Internet phone automatically receives a call even while it is not connected to the Internet through a dial-up connection (for example, Japanese Unexamined Patent Publication No. 2001-177663, paragraph [0025] to [0028], FIG. 1).
In an environment where users can use both IP phones and mobile phones, a caller normally cannot know whether a receiver is near an IP phone. If the caller calls to an IP phone that is considered as being near the receiver and the receiver is not near the IP phone actually, the caller calls the receiver's mobile phone this time. This takes time and is troublesome.
Further, the IP phone network and the mobile phone network are independently set up. Therefore, there are only a few services to make a call from an IP phone to a mobile phone and the services use a gateway to connect the IP network and the mobile phone network. Since a charge for communication between an IP phone and a mobile phone is more expensive than that for communication between mobile phones, what a caller and a receiver who can both use IP phones have communication from an IP phone to a mobile phone is waste of money. In short, callers cannot effectively use the IP phones and the mobile phones if they cannot know whether receivers are near IP phones.
Note that the above-described conventional technique relates to a dial-up connection of Internet phones and is not considered for appropriate integration control of IP phones and mobile phones.